FIX: Dell Laptop – Operating System Loader signature not found/invalid. (Solved)

Last updated on February 18th, 2019

One of my customers, brought his Dell Inspiron 15-3567 laptop, to our service store with the following boot problem: "The Operating System Loader signature not found in SecureBoot database ('db'). All bootable devices failed Secure Boot verification." 

The "Operating System Loader signature not found" problem, shows up right after powering up the Dell laptop with Windows 10 OS and as a result of the problem is that the machine cannot boot to Windows.

DELL Operating System Loader signature not found.

The "Operating System Loader signature is invalid" & the "Operating System Loader signature not found" errors, are appeared after installing the Windows Update KB3172729, that affects Windows 8.1 and Windows 10 OS. The Update KB3172729, updates the SecureBoot and may cause the EFI boot partition to be mounted as a non-system disk, causing the DDPE (Dell Data Protection Encryption) to encrypt the files on that partition and the system unbootable.

In this tutorial you 'll find instructions to resolve the "Operating System Loader signature not found" boot issue on a Dell notebook.

How to fix Dell laptop issue: Operating System Loader signature not found.

Requirements: To fix the The "Operating System Loader signature not found" problem you need to start your PC from a Windows 10 Installation USB Media. If you don't own a Windows USB installation media, then (from another working pc) you can create one by using the Media Creation tool.

1. When the "Operating System Loader signature not found" appears on the laptop's screen, press the power button for 5-6 seconds to shutdown the laptop.
2. Plug the Windows USB installation media, on an empty USB port.
3. Power On your laptop and when the Dell logo appears on screen, press the F2 key (on you keyboard) to enter BIOS Setup.
4. Find the Secure Boot options and Disable the Secure Boot.
5. Save and Exit from BIOS Setup.

disable secure boot

6. When the Dell logo appears on screen, press the F12 key and then select the USB media from the list (and press Enter), to boot your system from the USB installation media.

7. At the Windows Language Setup screen press SHIFT + F10 to access command prompt, or choose Next –> Repair your computer –> Troubleshoot –> Advanced Options –> Command Prompt.

windows setup screen

8. In command prompt give these commands:

  • diskpart
  • list volume

9. Now notice the following information:

1. The Volume number of the EFI* volume (with size 350-500MB and FAT32 format) if you own an UEFI based system, or the Volume number of the System Rese * ("System Reserved") volume (with size 100-350MB and NTFS format) if you own a non UEFI system.

2. The drive Driver Letter of the OS Volume. **

* This Volume contains the volume contains the Boot Manager and the Boot Configuration Data.

** The OS volume is the partition where the Windows are installed and commonly is the largest volume in size (GB).

e.g. In this example (NON UEFI system):

The volume number of the "System Rese" volume is "2"

The drive letter of the OS volume is "D".

repair boot configuration

10a. Now select the volume that contains the Boot Configuration data, (e.g. the "System Rese" in this example), by typing this command: *

  • select volume 2

* Note: Replace the number "2", according to your case.

10b. Then give assign a drive letter to the selected volume, by typing this command:

  • assign letter=Z

11. Type exit to close DISKPART tool.

  • exit

12. Finally type the following command to repair the boot configuration data:

  • bcdboot D:\windows /s Z: /f ALL

* Note: Replace the letter "D", according to the drive letter of the OS volume in your case.

13. Restart your computer and try to boot in Windows normally. If Windows doesn't boot, then:

a. Boot again from the USB Windows media.

b. At the Windows Language Setup screen click Windows Language Setup screen, Next –> Repair your computer –> Troubleshoot –> Startup Repair.

fix Operating System Loader signature not found

c. Let Windows to repair the startup problems and then restart your computer, to boot normally to Windows.

14. After the successful boot, don't forget to re-enable the Secure Boot in BIOS Setup.

That's it! Let me know if this guide has helped you by leaving your comment about your experience. Please like and share this guide to help others.

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